Users of telecommunication systems use to be assigned to one or more identifiers. Such identifiers are intended to be used by other users for requesting communications, and can take various formats according to the specific telecommunication technology for which they where devised.
For example, E.164 numbers (ITU recommendation E.164, May 1997) (commonly known as “telephone numbers”) are usually used as identifiers in legacy telecommunication systems such as: PSTN (Public Switched Telephone Network), ISDN (Integrated Services Digital Network), or 2G (second generation) mobile systems. E.164 numbers where primarily defined for allowing routing telephony calls based on its numeric structure. So, for example, an E.164 number such as “+34 91 555 XXXX” could identify a user in Spain within the local area of Madrid.
Identifiers used in modern telecommunication systems providing, for example, multimedia services (such as: video conference, data transfer, multimedia messaging, etc., as well as traditional voice-only calls) use to align with URI (Uniform Resource Identifier) format. Usually, these modern systems support also legacy identifiers, such as E.164 numbers, for interworking purposes with legacy systems, as well as for keeping associated to the same user an old (legacy) identifier. URIs are well-known identifiers widely used by Internet application and services for identifying resources (either: abstract of physical entities). URIs are further divided as “locators” (Uniform Resource Locators, URLs) or “names” (Uniform Resource Names, URNs). As opposed to URNs, that are intended to merely name a resource (even when the resource itself ceases or becomes unavailable), URLs identifies a resource by its location in a network (i.e.: identifies and locates it). For the sake of a greater simplicity, and given that the abstract conceptual differences between URIs and URLs are tiny enough for considering them equivalent when referring string of characters that “identify” resources, the term URL shall be used hereinafter.
Nowadays, URLs are assigned as identifiers to a plurality of heterogeneous resources for which service requests can be received. For example, an URL can be used to identify a web page, an electronic mail account, a file downloadable file, etc. Identifiers associated to users that are served for a given service in a specific network domain, use to be URLs that has a format that comprises: a user-name portion and a domain-portion, separated by the separator character “@”. The domain-portion identifies the network domain serving a given user, who is named (and identified) as specified in the content of the user-name portion in said domain.
Telecommunication systems using a multimedia protocols, such as H.323 protocol (ITU-T recommendation H.323, November 2000) or SIP protocol (IETF RFC2543 “Session Initiation Protocol”, March 1999), use URLs to identify their users (among other type of identifiers). So, a user having a subscription with a telecommunications operator that owns a telecommunication system supporting a multimedia protocol such as SIP, uses to be assigned to an identifier having an URL format (known as SIP-URL) that identifies said user in the network domain of said operator; for example “sip:John.Doe@OperatorA.se”. Similarly, for other communication services, such as traditional telephony, fax, electronic mail, modem based data calls, etc., a plurality of URLs can be defined to reach the destination user in the corresponding service point according to the requested service (e.g.: a plain telephone, the inbox of a mail account, a fax machine, or a modem); for example: “tel:+98-7-6543210”, “mailto:John.Doe@OperatorA.se”, “fax:+98-7-6543210”, “modem:+98-7-6543210; type=v110”.
A given user having a subscription with a telecommunications operator can, depending on the capabilities of the telecommunication system of said operator, an also depending on his/her subscription characteristics, receive a plurality of telecommunication services, or just only one type of services, having subscribed other services with another operator.
For example, a user can have a subscription with Operator-A for basic telephony service, multimedia communication service and electronic mail service. Also, a user can have, for example, basic telephony and multimedia services subscribed with Operator-A, while keeping a subscription with Operator-B for solely multimedia service. An example of a telecommunication system able to provide a variety of telecommunication services and handle various kind of identifiers for users (including E.164 identifiers and URLs) is a 3G (third generation) mobile system having the, so called, IMS (Internet Protocol Multimedia Subsystem) for providing multimedia services.
E.164 identifiers have been widely used for identifying users of telecommunication systems providing telephony services; and, as mentioned above, many systems still use E.164 identifiers as the only type of identifier that a user (originating user) can use for requesting a communication service towards another user (destination user). The appearance of new telecommunication services made traditional telephony operators to offer some of these new services to their users. Among reasons such as: to allow an smooth migration towards a new telecommunication service replacing an equivalent old one (e.g.: a multimedia service in replacement of a traditional voice-only telephony service), and to avoid user's inconvenience of publishing his/her new identifier(s) for the new service(s) subscribed; a given user subscribes a new service with his/her operator, uses to keep his/her old E.164 identifier associated also to this new subscription. So, for example, a given operator owning a 2G system and a 3G system with IMS, allows users subscribed to its 2G system to migrate their subscription to its 3G system while keeping their old E.164 identifiers. This allow these users to receive services from other legacy telecommunication systems, such as for example, calls or SMS (Short Messages) that are originally addressed using E.164 identifiers.
When routing a service request to its destination user that contains an E.164 as identifier for said user, for some telecommunication systems (or for some parts of said system through which a certain protocol is used for signaling the service) said E.164 identifier can be found as not suitable for routing and/or identification purposes. Also, in a given point of the execution of a service request, it can be desirable to select a service point (e.g.: a given terminal of the destination user) where to finally deliver the service, being said user identified in said terminal with an identifier which is not the same as the one received in the service request.